1. Field of Invention
This invention relates to a method and apparatus for stretching plastic material, and, more particularly, to a method and apparatus for stretching dough for bread or confectionery.
2. Description of Prior Art
Before now plastic materials or dough for bread or confectionery have been continuously stretched by supplying the dough to the clearance between a conveyor and a fixed roller.
Although such a fixed roller is not used in it, U.S. Pat. No. 4,692,110 discloses an apparatus for stretching dough in which a plurality of conveyors, each being driven at a different speed, are serially disposed. In it a roller mechanism comprising a plurality of rollers that are freely rotatable about their axes, and that constitute a straight path, is located above and spaced apart from the serially disposed portion of the conveyors. Since in these prior apparatuses the conveying speed of the downstream conveyor is higher than that of the upstream conveyor, and the dough being conveyed by the serially disposed conveyors is gently held and stretched by the rollers that are advancing downstream or reciprocating over the surface of the dough, the dough is effectively stretched.
However, the roller mechanism of this U.S. patent has a heavy and complex structure. Since this roller mechanism is heavy, the mechanism can perform only 40 strokes per minute when the stroke distance is 500 mm, and the structural complexity requires high production, maintenance, and repair costs. Therefore, an apparatus for stretching dough that is simple, functions steadily, and that has low production costs, has been desired.